(1) Technical Field
The present invention relates to a method of making a resin-molded magnetic core part for use in electronic instruments or electric instruments such as, for example, inductors, transformers, antennas (bar antennas), choke coils, filters, sensors, and the like.
(2) Background Art
In recent years, there is a growing tendency for an electronic or electric instrument to be reduced in size or increased in frequency or electric current and, hence, a core part is similarly required to respond to such tendency. However, ferrite material that is most frequently used has reached a limit in terms of material characteristics, and a new material is being sought. In some cases, ferrite material is replaced with a new material such as, for example, Sendust or amorphous foil strip. Although amorphous powder material superior in magnetic properties appears, it is inferior in moldability or compactibility to the conventional material, and the practical use thereof is accordingly limited.
In order to miniaturize the core part, a magnetic part (coil-embedded magnetic part) having a coil united with magnetic powder has been proposed. In making such a magnetic part, a green compact is first formed having electrode terminals that protrude outwardly from a side surface thereof. When the electrode terminals are then bent, there is a good chance that cracks may occur in the green compact around the portions from which the electrode terminals are led out or the green compact may break. In view of this, an improved coil-embedded magnetic part has been proposed having two or more terminals that protrude from a side surface of a powder compact, wherein recesses are formed in upper and lower surfaces of the green compact immediately above and below the leading positions of the terminals so as to be wider than the terminals. By so doing, the density of the compact around the leading portions of the terminals is increased, thereby preventing the occurrence of cracks or the breakage of the compact, which may be caused by the bending of the terminals (see, for example, Patent Document 1).
Further, in a method of making a rotor for a small motor that is provided with a rotary shaft and a permanent magnet united together by insert molding in which a resinous material is used, the productivity is increased using a resin containing a soft magnetic material during the insert molding (see, for example, Patent Document 2).
Another proposal has been offered wherein an integrated core is formed by first punching a lead frame having a carrier portion and terminal portions from a strip-shaped metal plate, subsequently bending ends of the terminal portions, and insert molding the lead frame with the use of ferrite resin with the terminal portions partly exposed (see, for example, Patent Document 3).
A further proposal has been also offered wherein the magnetic properties are enhanced by mixing permanent magnet pieces and an insulating material, compression molding a resulting mixture into a magnet, and inserting the magnet in a space defined in a magnetic core (see, for example, Patent Document 4).
Patent Document 1: Japanese Laid-Open Patent Publication No. 2003-309024
Patent Document 2: Japanese Laid-Open Patent Publication No. 10-257701
Patent Document 3: Japanese Laid-Open Patent Publication No. 5-315176
Patent Document 4: Japanese Laid-Open Patent Publication No. 50-133453